Speed reducer for walk assist apparatus

ABSTRACT

A reduction gear ( 49 ) for a walking assistance system is provided that includes first to third planetary gear mechanisms (P 1  to P 3 ) between an input shaft (Si) connected to a motor ( 48 ) and an output shaft (So), the second planetary gear mechanism (P 2 ) being disposed radially outside the first planetary gear mechanism (P 1 ) connected to the input shaft (Si), and the third planetary gear mechanism (P 3 ) being disposed outside, in the direction of an axis L, the first planetary gear mechanism (P 1 ). It is therefore possible, while reducing the speed of rotation of the input shaft (Si) in three stages by the first to the third planetary gear mechanisms (P 1  to P 3 ) and transmitting the rotation to the output shaft (So), to reduce the thickness of the reduction gear ( 49 ) compared with a case in which the first to the third planetary gear mechanisms (P 1  to P 3 ) are disposed so as to be stacked in the direction of the axis (L), thereby improving the appearance when a user is fitted with the walking assistance system.

FIELD OF THE INVENTION

The present invention relates to a walking assistance system thatassists elderly people with weakened muscle strength or injured peopleto walk, climb up and down stairs, stand up from a seated posture, sitdown from a standing posture, etc. so as to facilitate movement, thussuppressing degradation in muscle strength and correcting the gait mode,and, in particular, it relates to a reduction gear for the walkingassistance system.

BACKGROUND ART

Such a walking assistance system has already been proposed in JapanesePatent Application No. 2001-109046 related to an application of thepresent applicant. This walking assistance system includes an electricactuator fitted to user's leg joints (i.e., a hip joint and a knee joint), and the actuator is operated by supplying electric power from a powersource within a backpack carried by the user on the back so as togenerate a joint torque for extending/bending each joint, thus assistingthe user in carrying out a movement such as walking.

Furthermore, a reduction gear in which a plurality of planetary gearmechanisms are axially stacked in multiple stages so as to achieve alarge reduction ratio with a small size is known from Japanese PatentApplication Laid-open No. 8-247225 and Japanese Patent ApplicationLaid-open No. 11-37226.

The above-mentioned conventional walking assistance system includes anactuator integrated with a motor and a reduction gear, and since thereduction gear is required to have a large reduction ratio, there is theproblem that the overall dimensions of the actuator increase. As aresult, it becomes difficult to fit the actuator under a user'sclothing, and since the actuator is exposed outside the clothing, theappearance is poor.

Although the above-mentioned conventional reduction gear, in which theplurality of planetary gear mechanisms are axially stacked in multiplestages, is excellent in having a large reduction ratio, since the axialdimensions are large, it is not suitable for use in an actuator of awalking assistance system.

DISCLOSURE OF INVENTION

The present invention has been accomplished under the above-mentionedcircumstances, and it is an object thereof to achieve a thin reductiongear for a walking assistance system while ensuring that the reductiongear has a sufficient reduction ratio.

In order to attain this object, in accordance with a first aspect of thepresent invention, there is proposed a reduction gear for a walkingassistance system that, in order to assist walking movement byextending/bending a user's leg joint, reduces the speed of rotation ofan input shaft driven by a motor and transmits the rotation to an outputshaft connected to the leg joint, the reduction gear including the inputshaft, the output shaft, a first planetary gear mechanism, and a secondplanetary gear mechanism disposed coaxially on an axis, the secondplanetary gear mechanism being disposed so as to substantially overlapthe radially outer side of the first planetary gear mechanism, therotation of the input shaft being reduced in speed by the firstplanetary gear mechanism and the second planetary gear mechanism andtransmitted to the output shaft, the first planetary gear mechanismincluding a first sun gear provided on the input shaft, a first ringgear rotatably disposed so as to surround the outer periphery of thefirst sun gear, a plurality of first planetary gears meshingsimultaneously with the first sun gear and the first ring gear, and afirst carrier rotatably supporting the first planetary gears, and thesecond planetary gear mechanism including a second sun gear provided onthe outer periphery of the first ring gear, a second ring gear disposedso as to surround the outer periphery of the second sun gear, aplurality of second planetary gears meshing simultaneously with thesecond sun gear and the second ring gear, and a second carrier rotatablysupporting the second planetary gears.

In accordance with this arrangement, since the input shaft, the outputshaft, the first planetary gear mechanism, and the second planetary gearmechanism are disposed coaxially on the axis of the reduction gear forthe walking assistance system, and the second planetary gear mechanismis disposed so as to substantially overlap the radially outer side ofthe first planetary gear mechanism, it is possible, while reducing inspeed the rotation of the input shaft in two stages by the first andsecond planetary gear mechanisms and transmitting it to the outputshaft, to reduce the axial thickness of the reduction gear compared witha case in which the first and second planetary gear mechanisms aredisposed so as to be stacked in the axial direction, thereby improvingthe appearance when a user is equipped with the walking assistancesystem.

Furthermore, in accordance with a second aspect of the presentinvention, in addition to the first aspect, there is proposed thereduction gear for the walking assistance system wherein the firstcarrier of the first planetary gear mechanism is fixed to a casing, thesecond ring gear of the second planetary gear mechanism is fixed to thecasing, and the second carrier of the second planetary gear mechanism isconnected to the output shaft.

In accordance with this arrangement, fixing the first carrier of thefirst planetary gear mechanism to the casing enables the rotation inputfrom the first sun gear to be output from the first ring gear, andfixing the second ring gear to the casing enables the rotation inputinto the second sun gear, which is integral with the first ring gear, tobe output from the second carrier, thereby enabling the rotation of theinput shaft to be reduced in speed in two stages by the first and secondplanetary gear mechanisms and transmitted to the output shaft.

Moreover, in accordance with a third aspect of the present invention, inaddition to the second aspect, there is proposed the reduction gear forthe walking assistance system wherein a third planetary gear mechanismis disposed so as to be coaxial with and axially be stacked on the firstplanetary gear mechanism and the second planetary gear mechanism, thethird planetary gear mechanism including a third sun gear provided onthe outer periphery of a central part of the second carrier of thesecond planetary gear mechanism, a third ring gear fixed to the casingand disposed so as to surround the outer periphery of the third sungear, a plurality of third planetary gears meshing simultaneously withthe third sun gear and the third ring gear, and a third carrierrotatably supporting the third planetary gears and connected to theoutput shaft.

In accordance with this arrangement, fixing to the casing the third ringgear of the third planetary gear mechanism, which is disposed so as tobe coaxial with and axially be stacked on the first and second planetarygear mechanisms, enables the rotation input into the third sun gear,which is integral with the second carrier, to be output to the thirdcarrier, thereby enabling the rotation of the input shaft to be reducedin speed in three stages by the first to the third planetary gearmechanisms and transmitted to the output shaft.

Furthermore, in accordance with a fourth aspect of the presentinvention, there is proposed a reduction gear for a walking assistancesystem that, in order to assist walking movement by extending/bending auser's leg joint, reduces the speed of rotation of an input shaft drivenby a motor and transmits the rotation to an output shaft connected tothe leg joint, the reduction gear including the input shaft, the outputshaft, a first planetary gear mechanism, a second planetary gearmechanism, and a third planetary gear mechanism disposed coaxially on anaxis, the second planetary gear mechanism being disposed so as tosubstantially overlap the radially outer side of the first planetarygear mechanism, the third planetary gear mechanism being disposed so asto substantially overlap the radially outer side of the second planetarygear mechanism, the rotation of the input shaft being reduced in speedby the first planetary gear mechanism, the second planetary gearmechanism, and the third planetary gear mechanism and transmitted to theoutput shaft, the first planetary gear mechanism including a first sungear provided on the input shaft, a first ring gear formed on the innerperiphery of an inside ring member rotatably disposed so as to surroundthe first sun gear, a plurality of first planetary gears meshingsimultaneously with the first sun gear and the first ring gear, and afirst carrier fixed to a casing and rotatably supporting the firstplanetary gears, the second planetary gear mechanism including a secondsun gear formed on the outer periphery of the inside ring member, asecond ring gear formed on the inner periphery of an outside ring memberdisposed so as to surround the outer periphery of the second sun gear, aplurality of second planetary gears meshing simultaneously with thesecond sun gear and the second ring gear, and a second carrier fixed tothe casing and rotatably supporting the second planetary gears, and thethird planetary gear mechanism including a third sun gear formed on theouter periphery of the outside ring member, a third ring gear fixed tothe casing so as to surround the outer periphery of the third sun gear,a plurality of third planetary gears meshing simultaneously with thethird sun gear and the third ring gear, and a third carrier rotatablysupporting the third planetary gears and connected to the output shaft.

In accordance with this arrangement, while the input shaft, the outputshaft, the first planetary gear mechanism, the second planetary gearmechanism, and the third planetary gear mechanism are disposed coaxiallyon the axis of the reduction gear for the walking assistance system,fixing the first carrier of the first planetary gear mechanism to thecasing enables the rotation input from the input shaft into the firstsun gear to be output from the first ring gear; fixing the secondcarrier to the casing enables the rotation input into the second sungear, which is integral with the first ring gear, to be output from thesecond ring gear; and fixing the third ring gear to the casing enablesthe rotation input into the third sun gear, which is integral with thesecond ring gear, to be output from the third carrier, thereby enablingthe rotation of the input shaft to be reduced in speed in three stagesby the first to the third planetary gear mechanisms and transmitted tothe output shaft. Furthermore, since the second planetary gear mechanismis disposed so as to substantially overlap the radially outer side ofthe first planetary gear mechanism, and the third planetary gearmechanism is disposed so as to substantially overlap the radially outerside of the second planetary gear mechanism, it is possible, whilereducing in speed the rotation of the input shaft in three stages by thefirst to the third planetary gear mechanisms and transmitting it to theoutput shaft, to reduce the axial thickness of the reduction gearcompared with a case in which the first to the third planetary gearmechanisms are all disposed so as to be stacked in the axial direction,thereby improving the appearance when the user is equipped with thewalking assistance system.

Moreover, in accordance with a fifth aspect of the present invention,there is proposed a reduction gear for a walking assistance system that,in order to assist walking movement by extending/bending a user's legjoint, reduces the speed of rotation of an input shaft driven by a motorand transmits the rotation to an output shaft connected to the legjoint, the reduction gear including the input shaft, the output shaft, afirst planetary gear mechanism, a lo second planetary gear mechanism,and a third planetary gear mechanism disposed coaxially on an axis, thesecond planetary gear mechanism being disposed so as to substantiallyoverlap the radially outer side of the first planetary gear mechanism,the third planetary gear mechanism being disposed so as to substantiallyoverlap the radially outer side of the second planetary gear mechanism,the rotation of the input shaft being reduced in speed by the firstplanetary gear mechanism, the second planetary gear mechanism, and thethird planetary gear mechanism and transmitted to the output shaft, thefirst planetary gear mechanism including a first sun gear provided onthe input shaft, a first ring gear fixed to a casing so as to surroundthe first sun gear, a plurality of first planetary gears meshingsimultaneously with the first sun gear and the first ring gear, and afirst carrier rotatably supporting the first planetary gears, the secondplanetary gear mechanism including a second sun gear formed on the outerperiphery of the first carrier, a second ring gear fixed to the casingso as to surround the outer periphery of the second sun gear, aplurality of second planetary gears meshing simultaneously with thesecond sun gear and the second ring gear, and a second carrier rotatablysupporting the second planetary gears, and the third planetary gearmechanism including a third sun gear formed on the outer periphery ofthe second carrier, a third ring gear fixed to the casing so as tosurround the outer periphery of the third sun gear, a plurality of thirdplanetary gears meshing simultaneously with the third sun gear and thethird ring gear, and a third carrier rotatably supporting the thirdplanetary gears and connected to the output shaft.

In accordance with this arrangement, while the input shaft, the outputshaft, the first planetary gear mechanism, the second planetary gearmechanism, and the third planetary gear mechanism are disposed coaxiallyon the axis of the reduction gear for the walking assistance system,fixing the first ring gear of the first planetary gear mechanism to thecasing enables the rotation input from the first sun gear to be outputfrom the first carrier; fixing the second ring gear to the casingenables the rotation input into the second sun gear, which is integralwith the first carrier, to be output from the second carrier; and fixingthe third ring gear to the casing enables the rotation input to thethird sun gear, which is integral with the second carrier, to be outputfrom the third carrier, thereby enabling the rotation of the input shaftto be reduced in speed in three stages by the first to the thirdplanetary gear mechanisms and transmitted to the output shaft.Furthermore, since the second planetary gear mechanism is disposed so asto substantially overlap the radially outer side of the first planetarygear mechanism, and the third planetary gear mechanism is disposed so asto substantially overlap the radially outer side of the second planetarygear mechanism, it is possible, while reducing in speed the rotation ofthe input shaft in three stages by the first to the third planetary gearmechanisms and transmitting it to the output shaft, to reduce the axialthickness of the reduction gear compared with a case in which the firstto the third planetary gear mechanisms are all disposed so as to bestacked in the axial direction, thereby improving the appearance whenthe user is equipped with the walking assistance system.

Moreover, in accordance with a sixth aspect of the present invention,there is proposed a reduction gear for a walking assistance system that,in order to assist walking movement by extending/bending a user's legjoint, reduces the speed of rotation of an input shaft driven by a motorand transmits the rotation to an output shaft connected to the legjoint, the reduction gear including the input shaft, the output shaft, afirst planetary gear mechanism, a second planetary gear mechanism, and athird planetary gear mechanism disposed coaxially on an axis, the secondplanetary gear mechanism being disposed so as to substantially overlapthe radially outer side of the first planetary gear mechanism, the thirdplanetary gear mechanism being disposed so as to be stacked on the firstplanetary gear mechanism and the second planetary gear mechanism in theaxial direction, the rotation of the input shaft being reduced in speedby the first planetary gear mechanism, the second planetary gearmechanism, and the third planetary gear mechanism and transmitted to theoutput shaft, the first planetary gear mechanism including a first sungear provided on the input shaft, a first ring gear fixed to a casing soas to surround the outer periphery of the first sun gear, a plurality offirst planetary gears meshing simultaneously with the first sun gear andthe first ring gear, and a first carrier rotatably supporting the firstplanetary gears, the second planetary gear mechanism including a secondsun gear provided on the outer periphery of the first carrier, a secondring gear fixed to the casing so as to surround the outer periphery ofthe second sun gear, a plurality of second planetary gears meshingsimultaneously with the second sun gear and the second ring gear, and asecond carrier rotatably supporting the second planetary gears, and thethird planetary gear mechanism including a third sun gear provided onthe outer periphery of a central part of the second carrier, a thirdring gear fixed to the casing so as to surround the outer periphery ofthe third sun gear, a plurality of third planetary gears meshingsimultaneously with the third sun gear and the third ring gear, and athird carrier rotatably supporting the third planetary gears andconnected to the output shaft.

In accordance with this arrangement, while the input shaft, the outputshaft, the first planetary gear mechanism, the second planetary gearmechanism, and the third planetary gear mechanism are disposed coaxiallyon the axis of the reduction gear for the walking assistance system,fixing the first ring gear of the first planetary gear mechanism to thecasing enables the rotation input from the input shaft into the firstsun gear to be output from the first carrier; fixing the second ringgear to the casing enables the rotation input into the second sun gear,which is integral with the first carrier, to be output from the secondcarrier; and fixing the third ring gear to the casing enables therotation input into the third sun gear, which is integral with thesecond carrier, to be output from the third carrier, thereby enablingthe rotation of the input shaft to be reduced in speed in three stagesby the first to the third planetary gear mechanisms and transmitted tothe output shaft. Furthermore, since the second planetary gear mechanismis disposed so as to substantially overlap the radially outer side ofthe first planetary gear mechanism, and the third planetary gearmechanism is disposed so as to be stacked on the first planetary gearmechanism and the second planetary gear mechanism in the axialdirection, it is possible, while reducing in speed the rotation of theinput shaft in three stages by the first to the third planetary gearmechanisms and transmitting it to the output shaft, to reduce the axialthickness of the reduction gear compared with a case in which the firstto the third planetary gear mechanisms are all disposed so as to bestacked in the axial direction, thereby improving the appearance whenthe user is equipped with the walking assistance system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 to FIG. 7 show a first embodiment of the present invention; FIG.1 is a diagram showing a walking assistance system in use, FIG. 2 is afirst part view of an exploded perspective view of the walkingassistance system, FIG. 3 is a second part view of the explodedperspective view of the walking assistance system, FIG. 4 is a verticalsectional view of an electric actuator of the walking assistance system,FIG. 5 is a sectional view along line 5-5 in FIG. 4, FIG. 6 is asectional view along line 6-6 in FIG. 4, and FIG. 7 is a skeletondiagram of the electric actuator of the walking assistance system.

FIG. 8 to FIG. 10 show a second embodiment of the present invention;FIG. 8 is a vertical sectional view of an electric actuator of a walkingassistance system, FIG. 9 is a sectional view along line 9-9 in FIG. 8,and FIG. 10 is a skeleton diagram of the electric actuator of thewalking assistance system.

FIG. 11 to FIG. 13 show a third embodiment of the present invention;FIG. 11 is a vertical sectional view of an electric actuator of awalking assistance system, FIG. 12 is a sectional view along line 12-12in FIG. 11, and FIG. 13 is a skeleton diagram of the electric actuatorof the walking assistance system.

FIG. 14 to FIG. 17 show a fourth embodiment of the present invention;FIG. 14 is a vertical sectional view of an electric actuator of awalking assistance system, FIG. 15 is a sectional view along line 15-15in FIG. 14, FIG. 16 is a sectional view along line 16-16 in FIG. 14, andFIG. 17 is a skeleton diagram of the electric actuator of the walkingassistance system.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention is explained below withreference to FIG. 1 to FIG. 7.

As shown in FIG. 1 to FIG. 3, a walking assistance system of the presentinvention includes a backpack 11 carried by a user on the back, a pairof left and right first electric actuators 12 applying a torque to leftand right hip joints, a pair of left and right second electric actuators13 applying a torque to left and right knee joints, an abdominal belt 14made of a flexible resin and detachably fitted around the user'sabdomen, upper leg supports 15 f and 15 r made of a flexible resin,split into front and rear portions, and detachably fitted around theuser's left and right thighs, lower leg supports 16 f and 16 r made of aflexible resin, split into front and rear portions, and detachablyfitted around the user's left and right lower legs, and two suspenders17 extending from a front part of the abdominal belt 14 and connected toa rear part of the abdominal belt 14 via the user's shoulders. FIG. 3shows the upper leg supports 15 f and 15 r and the lower leg supports 16f and 16 r for a left leg, and those for a right leg, which are notillustrated, are laterally symmetrical and have the same structure.

A first link 18 and a reinforcing member 19 are secured by bolts so asto hold an outer face and an inner face of each of left and right sidesof the abdominal belt 14 therebetween. A second link 20 bendablyconnected to the lower end of the first link 18 via the first electricactuator 12 is secured by bolts to the outside of the rear upper legsupport 15 r. In this arrangement, a pivoting support for the first link18 and the second link 20, that is, the first electric actuator 12, ispositioned outside the user's hip joint.

An outside third link 21 and an inside third link 22 are secured bybolts to the outside and the inside respectively of the rear upper legsupport 15 r, and an outside fourth link 23 and an inside fourth link 24are secured by bolts to the outside and the inside respectively of therear lower leg support 16 r. The lower end of the outside third link 21and the upper end of the outside fourth link 23 are bendably connectedto each other via the second electric actuator 13, and the lower end ofthe inside third link 22 and the upper end of the inside fourth link 24are bendably connected to each other via a hinge 25. In thisarrangement, pivoting supports of the two third links 21 and 22 and thetwo fourth links 23 and 24, that is, the second electric actuator 13 andthe hinge 25, are positioned on the outside and the inside of the user'sknee joint.

Housed within the backpack 11, which is detachably fitted to thesuspenders 17, are an electronic control unit 26 for controlling theoperation of the first electric actuators 12 and the second electricactuators 13, an indicator 27 for indicating the state of torquegenerated by each of the actuators 12 and 13, a motor driver 28 fordriving a motor of each of the actuators 12 and 13, and a power source29 (e.g., an Ni—Zn battery) for supplying electric power to the motorsand the electronic control unit 26.

The first electric actuators 12 and the second electric actuators 13have a common structure, and are formed from a DC motor and a reductiongear, a casing thereof is secured by bolts to the lower end of the firstlink 18, and an output shaft thereof is joined by a bolt 30 to the upperend of the second link 20. Driving the first electric actuator 12therefore generates a torque for rotating the second link 20 relative tothe first link 18, thus enabling the user's hip joint to beextended/bent. Furthermore, the second electric actuator 13 has a casingthereof secured by bolts to the lower end of the outside third link 21and an output shaft thereof joined to the upper end of the outsidefourth link 23 by a bolt 30. Driving the second electric actuator 13therefore generates a torque for rotating the outside fourth link 23relative to the outside third link 21, thus enabling the user's kneejoint to be extended/bent.

The structure of the first electric actuator 12 is now explained withreference to FIG. 4 to FIG. 7. The structure of the second electricactuator 13 is the same as that of the first electric actuator 12.

A casing 41 of the first electric actuator 12 is formed in a bottomedcylindrical shape having an axis L as the center. The casing 41 isformed by layering a first support ring 42, a second support ring 43, asupport plate 44, a motor housing 45, and a motor cover 46 andintegrally securing them with a plurality of bolts 47. A motor 48 ishoused within the motor housing 45 and the motor cover 46, and areduction gear 49 is housed within the first support ring 42 and thesecond support ring 43. An input shaft Si of the reduction gear 49 issupported on the support plate 44 and the motor housing 45 via ballbearings 50 and 51, a rotor 52 of the motor 48 is fixed to the inputshaft Si, is and a stator 53 surrounding the outer periphery of therotor 52 is fixed to the motor housing 45. A permanent magnet 52 a and acoil 53 a are provided on the rotor 52 and the stator 53 respectively,and when the coil 53 a is energized, the input shaft Si rotates togetherwith the rotor 52.

The reduction gear 49 includes a first planetary gear mechanism P₁ and asecond planetary gear mechanism P₂ housed inside the second support ring43, and a third planetary gear mechanism P₃ housed inside the firstsupport ring 42. The first planetary gear mechanism P₁ is disposedradially inside the second planetary gear mechanism P₂, and the thirdplanetary gear mechanism P₃ is disposed outside, in the axis Ldirection, the first and second planetary gear mechanisms P₁ and P₂.

The first planetary gear mechanism P₁ includes a first sun gear ZS₁, afirst ring gear ZR₁, a plurality of first planetary gears ZP₁, and afirst carrier C₁. The first sun gear ZS₁ is connected to a shaft end ofthe input shaft Si via an electromagnetic clutch 54. The first ring gearZR₁ is formed integrally with the inner periphery of a ring member 55disposed rotatably around the axis L. The first carrier C₁, whichrotatably supports the first planetary gears ZP₁ meshing simultaneouslywith the first sun gear ZS₁ and the first ring gear ZR₁, is formed aspart of the support plate 44. The first planetary gear mechanism P₁ istherefore of a star type in which the first carrier C₁ is fixed and thefirst ring gear ZR₁ is rotatable, and when the first sun gear ZS₁, whichis connected to the input shaft Si via the electromagnetic clutch 54,rotates, the rotation is reduced in speed and reversed, and output tothe first ring gear ZR₁ (i.e., the ring member 55).

The reduction ratio of the star type first planetary gear mechanism P₁is defined as nr₁/ns₁, where ns, is an input rotational speed of thefirst sun gear ZS₁ and nr₁ is an output rotational speed of the firstring gear ZR₁. If zs₁, zr₁, is and zp₁ denote the number of teeth of thefirst sun gear ZS₁, the first ring gear ZR₁, and the first planetarygear ZP₁ respectively, the reduction ratio nr₁/ns₁ is given bynr ₁ /ns ₁ =−zs ₁ /zr ₁.   (1)The minus sign of the right-hand side of Equation (1) indicates that thedirection of rotation of the first ring gear ZR₁ is opposite to thedirection of rotation of the first sun gear ZS₁.

The second planetary gear mechanism P₂ includes a second sun gear ZS₂, asecond ring gear ZR₂, a plurality of second planetary gears ZP₂, and asecond carrier C₂. The second sun gear ZS₂ is formed on the outerperiphery of the ring member 55, on the inner periphery of which isformed the first ring gear ZR₁. The second ring gear ZR₂ is formedintegrally with the inner periphery of the second support ring 43, whichis fixed to the casing 41. The second carrier C₂, which rotatablysupports the second planetary gears ZP₂ meshing simultaneously with thesecond sun gear ZS₂ and the second ring gear ZR₂, is rotatably supportedon the inner periphery of the second support ring 43 via a ball bearing56. The second planetary gear mechanism P₂ is therefore of a planetarytype in which the second ring gear ZR₂ is fixed and the second carrierC₂ is rotatable, and when the second sun gear ZS₂, which is an inputmember, rotates, the rotation is reduced in speed and output in the samerotational sense to the second carrier C₂.

The reduction ratio of the planetary type second planetary gearmechanism P₂ is defined as nc₂/ns₂, where ns₂ is an input rotationalspeed of the second sun gear ZS and nc₂ is an output rotational speed ofthe second carrier C₂. If zs₂, zr₂, and zp₂ denote the number of teethof the second sun gear ZS₂, the second ring gear ZR₂, and the secondplanetary gear ZP₂ respectively, the reduction ratio nc₂/ns₂ is given bync ₂ /ns ₂ =zs ₂/(zs ₂ +zr ₂).   (2)

The third planetary gear mechanism P₃ includes a third sun gear ZS₃, athird ring gear ZR₃, a plurality of third planetary gears ZP₃, and athird carrier C₃. The third sun gear ZS₃ is formed integrally with theouter periphery of a central part of the second carrier C₂ of the secondplanetary gear mechanism P₂. The third ring gear ZR₃ is formedintegrally with the inner periphery of the first support ring 42, whichis fixed to the casing 41. The third carrier C₃, which rotatablysupports the third planetary gears ZP₃ meshing simultaneously with thethird sun gear ZS₃ and the third ring gear ZR₃, is rotatably supportedon the inner periphery of the first support ring 42 via a ball bearing57. The third planetary gear mechanism P₃ is therefore of a planetarytype in which the third ring gear ZR₃ is fixed and the third carrier C₃is rotatable, and when the third sun gear ZS₃, which is an input member,rotates, the rotation is reduced in speed and output in the samerotational sense to the output shaft So, which is integral with thethird carrier C₃.

The reduction ratio of the planetary type third planetary gear mechanismP₃ is defined as nc₃/ns₃, where ns₃ denotes an input rotational speed ofthe third sun gear ZS₃ and nc₃ denotes an output rotational speed of thethird carrier C₃. If zs₃, zr₃, and zp₃ denote the number of teeth of thethird sun gear ZS₃, the third ring gear ZR₃, and the third planetarygear ZP₃ respectively, the reduction ratio nc₃/ns₃ is given bync ₃ /ns ₃ =zs ₃/(zs₃ +zr ₃).   (3)

Since the output rotational speed nr₁ of the first ring gear ZR₁, whichis the output member of the first planetary gear mechanism P₁, is equalto the input rotational speed ns₂ of the second sun gear ZS₂, which isthe input member of the second planetary gear mechanism P₂, and theoutput rotational speed nc₂ of the second carrier C₂, which is theoutput member of the second planetary gear mechanism P₂, is equal to theinput rotational speed ns₃ of the third sun gear ZS₃, which is the inputmember of the third planetary gear mechanism P₃, the product of thereduction ratio nr₁/ns₁ of the first planetary gear mechanism P₁ shownin Equation (1), the reduction ratio nc₂/ns₂ of the second planetarygear mechanism P₂ shown in Equation (2), and the reduction ratio nc₃/ns₃of the third planetary gear mechanism P₃ shown in Equation (3) is givenby the ratio nc₃/ns₁ of the rotational speed nc₃ of the third carrier C₃of the third planetary gear mechanism P₃, the third carrier C₃ being theoutput member of the reduction gear 49, relative to the rotational speedns₁ of the first sun gear ZS₁ of the first planetary gear mechanism P₁,the first sun gear ZS₁ being the input member of the reduction gear 49.(nr ₁ /ns ₁)×(nc ₂ /ns ₂)×(nc ₃ /ns ₃)=nc ₃ /ns ₁   (4)

From Equation (1) to Equation (3), the reduction ratio nc₃/ns₁ of thereduction gear 49 is given bync ₃ /ns ₁=(−zs ₁ /zr ₁)×{zs ₂/(zs ₂ +zr ₂)}×{zs ₃/(zs ₃ +zr ₃)}  (5)and in the embodiment, since the number of teeth of each gear is set asfollows:

zs₁ = 18 zp₁ = 27 zr₁ = 72 zs₂ = 96 zp₂ = 24 zr₂ = 144 zs₃ = 36 zp₃ = 54zr₃ = 144,the reduction ratio nc₃/ns₁ of the reduction gear 49 obtained bysubstituting these numbers of teeth in Equation (5) is 1/50. That is,when the input shaft Si of the reduction gear 49 rotates 50 times, theoutput shaft So rotates once in the opposite direction.

As hereinbefore described, since the reduction gear 49 is formed byconnecting the first to the third planetary gear mechanisms P₁ to P₃, itis possible to increase the torque of the motor 48 while ensuring thatthere is a sufficient reduction ratio. Furthermore, since the secondplanetary gear mechanism P₂ is disposed so as to overlap the radiallyouter side of the first planetary gear mechanism P₁, it is possible toreduce the thickness in the axis L direction of the reduction gear 49compared with a case in which the first to the third planetary gearmechanisms P₁ to P₃ are all disposed so as to be stacked in the axis Ldirection. That is, the first electric actuators 12 and the secondelectric actuators 13 can be made compact by suppressing the thicknessof the reduction gear 49 to a thickness corresponding to two planetarygear mechanisms while ensuring that there is a reduction ratiocorresponding to three planetary gear mechanisms, thereby enablingfitting under a user's clothing with a good appearance.

The structure of a first electric actuator 12 related to a secondembodiment of the present invention is now explained with reference toFIG. 8 to FIG. 10. The structure of a second electric actuator 13 is thesame as that of the first electric actuator 12.

A casing 41 of the first electric actuator 12 is formed in a bottomedcylindrical shape having an axis L as the center. The casing 41 isformed by layering a support ring 42, a support plate 44, a motorhousing 45, and a motor cover 46 and integrally securing them with aplurality of bolts 47. A motor 48 is housed within the motor housing 45and the motor cover 46, and a reduction lo gear 49 is housed within thesupport ring 42. An input shaft Si of the reduction gear 49 is supportedon the support plate 44 and the motor cover 46 via ball bearings 50 and51, a rotor 52 of the motor 48 is fixed to the input shaft Si, and astator 53 surrounding the outer periphery of the rotor 52 is fixed tothe motor housing 45. A permanent magnet 52 a and a coil 53 a areprovided on the rotor 52 and the stator 53 respectively, and when thecoil 53 a is energized, the input shaft Si rotates together with therotor 52.

The reduction gear 49, which is housed within the support ring 42,includes a first planetary gear mechanism P₁, a second planetary gearmechanism P₂, and a third planetary gear mechanism P₃; the secondplanetary gear mechanism P₂ is disposed radially outside the firstplanetary gear mechanism P₁, and the third planetary gear mechanism P₃is disposed radially outside the second planetary gear mechanism P₂.

The first planetary gear mechanism P₁ includes a first sun gear ZS₁, afirst ring gear ZR₁, a plurality of first planetary gears ZP₁, and afirst carrier C₁. The first sun gear ZS₁ is connected to a shaft end ofthe input shaft Si via an electromagnetic clutch 54. The first ring gearZR₁ is formed integrally with the inner periphery of an inside ringmember 55 i disposed so as to surround the axis L. The first carrier C₁,which rotatably supports the first planetary gears ZP₁ meshingsimultaneously with the first sun gear ZS₁ and the first ring gear ZR₁,is provided as a portion close to the center of the support plate 44.The first planetary gear mechanism P₁ is therefore of a star type inwhich the first ring gear ZR₁ is rotatable and the first carrier C₁ isfixed, and when the first sun gear ZS₁, which is connected to the inputshaft Si via the electromagnetic clutch 54, rotates, the rotation isreduced in speed and reversed, and output to the first ring gear ZR₁.

The reduction ratio of the star type first-planetary gear mechanism P₁is defined as nr₁/ns₁, where ns₁ is an input rotational speed of thefirst sun gear ZS₁ and nr₁ is an output rotational speed of the firstring gear ZR₁. If zs₁, zr₁, and zp₁ denote the number of teeth of thefirst sun gear ZS₁, the first ring gear ZR₁, and the first planetarygear ZP₁ respectively, the reduction ratio nr₁/ns₁ is given bynr ₁ /ns ₁ =−zs ₁ /zr ₁.   (6)The minus sign of the right side of Equation (6) indicates that thedirection of rotation of the first ring gear ZR₁ is opposite to thedirection of rotation of the first sun gear ZS₁.

The second planetary gear mechanism P₂ includes a second sun gear ZS₂, asecond ring gear ZR₂, a plurality of second planetary gears ZP₂, and asecond carrier C₂. The second sun gear ZS₂ is formed on the outerperiphery of the inside ring member 55 i. The second ring gear ZR₂ isformed integrally with the inner periphery of an outside ring member 55o disposed so as to surround the axis L. The second carrier C₂, whichrotatably supports the second planetary gears ZP₂ meshing simultaneouslywith the second sun gear ZS₂ and the second ring gear ZR₂, is providedas a portion close to the outer periphery of the support plate 44. Thesecond planetary gear mechanism P₂ is therefore of a star type in whichthe second ring gear ZR₂ is rotatable and the second carrier C₂ isfixed, and when the second sun gear ZS₂, which is integral with thefirst ring gear ZR₁, rotates, the rotation is reduced in speed andreversed, and output to the second ring gear ZR₂.

The reduction ratio of the star type second planetary gear mechanism P₂is defined as nr₂/ns₂, where ns₂ is an input rotational speed of thesecond sun gear ZS₂ and nr₂ is an output rotational speed of the secondring gear ZR₂. If zs₂, zr₂, and zp₂ denote the number of teeth of thesecond sun gear ZS₂, the second ring gear ZR₂, and the second planetarygear ZP₂, respectively, the reduction ratio nr₂/ns₂ is given bynr ₂ /ns ₂ =−zs ₂ /zr ₂.   (7)The minus sign of the right-hand side of Equation (7) indicates that thedirection of rotation of the second ring gear ZR₂ is opposite to thedirection of rotation of the second sun gear ZS₂.

The third planetary gear mechanism P₃ includes a third sun gear ZS₃, athird ring gear ZR₃, a plurality of third planetary gears ZP₃, and athird carrier C₃. The third sun gear ZS₃ is formed integrally with theouter periphery of the outside ring member 55 o. The third ring gear ZR₃is formed integrally with the inner periphery of the support ring 42,which is fixed to the casing 41. The third carrier C₃, which rotatablysupports the third planetary gears ZP₃ meshing simultaneously with thethird sun gear ZS₃ and the third ring gear ZR₃, is rotatably supportedon the inner periphery of the support ring 42 via a ball bearing 57. Thethird planetary gear mechanism P₃ is therefore of a planetary type inwhich the third ring gear ZR₃ is fixed and the third carrier C₃ isrotatable, and when the third sun gear ZS₃, which is an input member,rotates, the rotation is reduced in speed in the same direction andoutput to the output shaft So, which is integral with the third carrierC₃.

The reduction ratio of the planetary type third planetary gear mechanismP₃ is defined as nc₃/ns₃, where ns₃ denotes an input rotational speed ofthe third sun gear ZS₃ and nc₃ denotes an output rotational speed of thethird carrier C₃. If zs₃, zr₃, and zp₃ denote the number of teeth of thethird sun gear ZS₃, the third ring gear ZR₃, and the third planetarygear ZP₃ respectively, the reduction ratio nc₃/ns₃ is given bync ₃ /ns ₃ =zs ₃/(zs₃ +zr ₃).   (8)

Since the output rotational speed nr₁ of the first ring gear ZR₁, whichis the output member of the first planetary gear mechanism P₁, is equalto the input rotational speed ns₂ of the second sun gear ZS₂, which isthe input member of the second planetary gear mechanism P₂, and theoutput rotational speed nr₂ of the second ring gear ZR₂, which is theoutput member of the second planetary gear mechanism P₂, is equal to theinput rotational speed ns₃ of the third sun gear ZS₃, which is the inputmember of the third planetary gear mechanism P₃, the product of thereduction ratio nr₁/ns₁ of the first planetary gear mechanism P₁ shownin Equation (6), the reduction ratio nr₂/ns₂ of the second planetarygear mechanism P₂ shown in Equation (7), and the reduction ratio nc₃/ns₃of the third planetary gear mechanism P₃ shown in Equation (8) is givenby the ratio nc₃/ns₁ of the rotational speed nc₃ of the third carrier C₃of the third planetary gear mechanism P₃, the third carrier C₃ being theoutput member of the reduction gear 49, relative to the rotational speedns₁ of the first sun gear ZS₁ of the first planetary gear mechanism P₁,the first sun gear ZS₁ being the input member of the reduction gear 49.(nr ₁ /ns ₁)×(nr ₂ /ns ₂)×(nc ₃ /ns ₃)=nc ₃ /ns ₁   (9)

From Equation (6) to Equation (8), the reduction ratio nc₃/ns₁ of thereduction gear 49 is given bync ₃ /ns ₁=(−zs ₁ /zr ₁)×(−zs ₂ /zr ₂)×{zs ₃/(zs₃ +zr ₃)}  (10)and in the embodiment, since the number of teeth of each gear is set asfollows:

zs₁ = 18 zp₁ = 27 zr₁ = 72 zs₂ = 96 zp₂ = 24 zr₂ = 144 zs₃ = 168 zp₃ =24 zr₃ = 216,the reduction ratio nc₃/ns₁ of the reduction gear 49 obtained bysubstituting these numbers of teeth in Equation (10) is 1/13.7. That is,when the input shaft Si of the reduction gear 49 rotates 13.7 times, theoutput shaft So rotates once in the same direction.

As hereinbefore described, since the reduction gear 49 is formed byconnecting the first to the third planetary gear mechanisms P₁ to P₃, itis possible to increase the torque of the motor 48 while ensuring thatthere is a sufficient reduction ratio. Furthermore, since the secondplanetary gear mechanism P₂ is disposed so as to overlap the radiallyouter side of the first planetary gear mechanism P₁, and the thirdplanetary gear mechanism P₃ is disposed so as to overlap the radiallyouter side of the second planetary gear mechanism P₂, it is possible toreduce the thickness in the axis L direction of the reduction gear 49compared with a case in which the first to the third planetary gearmechanisms P₁ to P₃ are all disposed so as to be stacked in the axis Ldirection. That is, the first electric actuators 12 and the secondelectric actuators 13 can be made compact by suppressing the thicknessof the reduction gear 49 to a thickness corresponding to one planetarygear mechanism while ensuring that there is a reduction ratiocorresponding to three planetary gear mechanisms, thereby enablingfitting under a user's clothing with a good appearance.

The structure of a first electric actuator 12 related to a thirdembodiment of the present invention is now explained with reference toFIG. 11 to FIG. 13. The structure of a second electric actuator 13 isthe same as that of the first -electric actuator 12.

A casing 41 of the first electric actuator 12 is formed in a bottomedcylindrical shape having an axis L as the center. The casing 41 isformed by layering a support ring 42, a support plate 44, a motorhousing 45, and a motor cover 46 and integrally securing them with aplurality of bolts 47. A motor 48 is housed within the motor housing 45and the motor cover 46, and a reduction gear 49 is housed within thesupport ring 42 and the support plate 44. An input shaft Si of thereduction gear 49 is supported on the support plate 44 and the motorcover 46 via ball bearings 50 and 51, a rotor 52 of the motor 48 isfixed to the input shaft Si, and a stator 53 surrounding the outerperiphery of the rotor 52 is fixed to the motor housing 45. A permanentmagnet 52 a and a coil 53 a are provided on the rotor 52 and the stator53 respectively, and when the coil 53 a is energized, the input shaft Sirotates together with the rotor 52.

The reduction gear 49, which is housed within the support ring 42,includes a first planetary gear mechanism P₁, a second planetary gearmechanism P₂, and a third planetary gear mechanism P₃; the secondplanetary gear mechanism P₂ is disposed radially outside the firstplanetary gear mechanism P₁, and the third planetary gear mechanism P₃is disposed radially outside the second planetary gear mechanism P₂.

The first planetary gear mechanism P₁includes a first sun gear ZS₁, afirst ring gear ZR₁, a plurality of first planetary gears ZP₁, and afirst carrier C₁. The first sun gear ZS₁ is connected to a shaft end ofthe input shaft Si via an electromagnetic clutch 54. The first ring gearZR₁ is formed integrally at a position close to the center of thesupport plate 44 so as to surround the axis L. The first carrier C₁,which rotatably supports the first planetary gears ZP₁ meshingsimultaneously with the first sun gear ZS₁ and the first ring gear ZR₁,is disposed rotatably around the axis L. The first planetary gearmechanism P₁ is therefore of a planetary type in which the first ringgear ZR₁ is fixed and the first carrier C₁ is rotatable, and when thefirst sun gear ZS₁, which is connected to the input shaft Si via theelectromagnetic clutch 54, rotates, the rotation is reduced in speed inthe same direction, and output to the first carrier C₁.

The reduction ratio of the planetary type first planetary gear mechanismP₁ is defined as nc₁/ns₁, where ns₁ is an input rotational speed of thefirst sun gear ZS₁ and nc₁ is an output rotational speed of the firstcarrier C₁. If zs₁, zr₁, and zp₁ denote the number of teeth of the firstsun gear ZS₁, the first ring gear ZR₁, and the first planetary gear ZP₁respectively, the reduction ratio nc₁/ns₁ is given bync ₁ /ns ₁ =zs ₁/(zs ₁ +zr ₁).   (11)

The second planetary gear mechanism P₂ includes a second sun gear ZS₂, asecond ring gear ZR₂, a plurality of second planetary gears ZP₂, and asecond carrier C₂. The second sun gear ZS₂ is formed on the outerperiphery of the first carrier C₁ of the first planetary gear mechanismP₁. The second ring gear ZR₂ is formed at a position close to the outerperiphery of the support plate 44 so as to surround the axis L. Thesecond carrier C₂, which rotatably supports the second planetary gearsZP₂ meshing simultaneously with the second sun gear ZS₂ and the secondring gear ZR₂, is disposed rotatably around the axis L. The secondplanetary gear mechanism P₂ is therefore of a planetary type in whichthe second ring gear ZR₂ is fixed and the second carrier C₂ isrotatable, and when the second sun gear ZS₂ rotates, the rotation isreduced in speed in the same direction, and output to the second carrierC₂.

The reduction ratio of the planetary type second planetary gearmechanism P₂ is defined as nc₂/ns₂, where ns₂ is an input rotationalspeed of the second sun gear ZS and nc₂ is an output rotational speed ofthe second carrier C₂. If zs₂, zr₂, and zp₂ denote the number of teethof the second sun gear ZS₂, the second ring gear ZR₂, and the secondplanetary gear ZP₂ respectively, the reduction ratio nc₂/ns₂ is given bync ₂/ns₂ =zs ₂/(zs ₂ +zr ₂).   (12)

The third planetary gear mechanism P₃ includes a third sun gear ZS₃, athird ring gear ZR₃, a plurality of third planetary gears ZP₃, and athird carrier C₃. The third sun gear ZS₃ is formed on the outerperiphery of the second carrier C₂ of the second planetary gearmechanism P₂. The third ring gear ZR₃ is formed integrally with theinner periphery of the support ring 42. The third carrier C₃, whichrotatably supports the third planetary gears ZP₃ meshing simultaneouslywith the third sun gear ZS₃ and the third ring gear ZR₃, is rotatablysupported on the inner periphery of the support ring 42 via a ballbearing 57. The third planetary gear mechanism P₃ is therefore of aplanetary type in which the third ring gear ZR₃ is fixed and the thirdcarrier C₃ is rotatable, and when the third sun gear ZS₃ rotates, therotation is reduced in speed in the same direction and output to theoutput shaft So, which is integral with the third carrier C₃.

The reduction ratio of the planetary type third planetary gear mechanismP₃ is defined as nc₃/ns₃, where ns₃ denotes an input rotational speed ofthe third sun gear ZS₃ and nc₃ denotes an output rotational speed of thethird carrier C₃. If zs₃, zr₃, and zp₃ denote the number of teeth of thethird sun gear ZS₃, the third ring gear ZR₃, and the third planetarygear ZP₃ respectively, the reduction ratio nc₃/ns₃ is given bync ₃ /ns ₃ =zs ₃/(zs₃ +zr ₃).   (13)

Since the output rotational speed nc₁ of the first carrier C₁, which isthe output member of the first planetary gear mechanism P₁, is equal tothe input rotational speed ns₂ of the second sun gear ZS₂, which is theinput member of the second planetary gear mechanism P₂, and the outputrotational speed nc₂ of the second carrier C₂, which is the outputmember of the second planetary gear mechanism P₂, is equal to the inputrotational speed ns₃ of the third sun gear ZS₃, which is the inputmember of the third planetary gear mechanism P₃, the product of thereduction ratio nc₁/ns₁ of the first planetary gear mechanism P₁ shownin Equation (11), the reduction ratio nc₂/ns₂ of the second planetarygear mechanism P₂ shown in Equation (12), and the reduction rationc₃/ns₃ of the third planetary gear mechanism P₃ shown in Equation (13)is given by the ratio nc₃/ns₁ of the rotational speed nc₃ of the thirdcarrier C₃ of the third planetary gear mechanism P₃, the third carrierC₃ being the output member of the reduction gear 49, relative to therotational speed ns₁ of the first sun gear ZS₁ of the first planetarygear mechanism P₁, the first sun gear ZS₁ being the input member of thereduction gear 49.(nc ₁ /ns ₁)×(nc ₂ /ns ₂)×(nc ₃ /ns ₃)=nc ₃ /ns ₁   (14)

From Equation (11) to Equation (13), the reduction ratio nc₃/ns₁ of thereduction gear 49 is given bync ₃ /ns ₁ ={zs ₁/(zs ₁ +zr ₁)}×{zs ₂/(zs ₂ +zr ₂)}×{zs ₃/(zs ₃ +zr₃)}  (15)and in the embodiment, since the number of teeth of each gear is set asfollows:

zs₁ = 18 zp₁ = 27 zr₁ = 72 zs₂ = 96 zp₂ = 24 zr₂ = 144 zs₃ = 168 zp₃ =24 zr₃ = 216,the reduction ratio nc₃/ns₁ of the reduction gear 49 obtained bysubstituting these numbers of teeth in Equation (15) is 1/28.5. That is,when the input shaft Si of the reduction gear 49 rotates 28.5 times, theoutput shaft So rotates once in the same direction.

As hereinbefore described, since the reduction gear 49 is formed byconnecting the first to the third planetary gear mechanisms P₁ to P₃, itis possible to increase the torque of the motor 48 while ensuring thatthere is a sufficient reduction ratio. Furthermore, since the secondplanetary gear mechanism P₂ is disposed so as to overlap the radiallyouter side of the first planetary gear mechanism P₁, and the thirdplanetary gear mechanism P₃ is disposed so as to overlap the radiallyouter side of the second planetary gear mechanism P₂, it is possible toreduce the thickness in the axis L direction of the reduction gear 49compared with a case in which the first to the third lo planetary gearmechanisms P₁ to P₃ are all disposed so as to be stacked in the axis Ldirection. That is, the first electric actuators 12 and the secondelectric actuators 13 can be made compact by suppressing the thicknessof the reduction gear 49 to a thickness corresponding to one planetarygear mechanism while ensuring that there is a reduction ratiocorresponding to three planetary gear mechanisms, thereby enablingfitting under a user's clothing with a good appearance.

The structure of a first electric actuator 12 related to a fourthembodiment of the present invention is now explained with reference toFIG. 14 to FIG. 17. The structure of a second electric actuator 13 isthe same as that of the first electric actuator 12.

A casing 41 of the first electric actuator 12 is formed in a bottomedcylindrical shape having an axis L as the center. The casing 41 isformed by layering a first support ring 42, a second support ring 43, asupport plate 44, a motor housing 45, and a motor cover 46 andintegrally securing them with a plurality of bolts 47. A motor 48 ishoused within the motor housing 45 and the motor cover 46, and areduction gear 49 is housed within the first support ring 42 and thesecond support ring 43. An input shaft Si of the reduction gear 49 issupported on the support plate 44 and the motor housing 45 via ballbearings 50 and 51, a rotor 52 of the motor 48 is fixed to the inputshaft Si, and a stator 53 surrounding the outer periphery of the rotor52 is fixed to the motor housing 45. A permanent magnet 52 a and a coil53 a are provided on the rotor 52 and the stator 53 respectively, andwhen the coil 53 a is energized, the input shaft Si rotates togetherwith the rotor 52.

The reduction gear 49 includes a first planetary gear mechanism P₁ and asecond planetary gear mechanism P₂ housed inside the second support ring43, and a third planetary gear mechanism P₃ housed inside the firstsupport ring 42. The first planetary gear mechanism P₁ is disposedradially inside the second planetary gear mechanism P₂, and the thirdplanetary gear mechanism P₃ is disposed outside, in the axis Ldirection, the first and second planetary gear mechanisms P₁ and P₂.

The first planetary gear mechanism P₁ includes a first sun gear ZS₁, afirst ring gear ZR₁, a plurality of first planetary gears ZP₁, and afirst carrier C₁. The first sun gear ZS₁ is connected to a shaft end ofthe input shaft Si via an electromagnetic clutch 54. The first ring gearZR₁ is formed integrally with the support plate 44 so as to surround theaxis L. The first carrier C₁, which rotatably supports the firstplanetary gears ZP₁ meshing simultaneously with the first sun gear ZS₁and the first ring gear ZR₁, is disposed rotatably around the axis L.The first planetary gear mechanism P₁ is therefore of a planetary typein which the first ring gear ZR₁ is fixed and the first carrier C₁ isrotatable, and when the first sun gear ZS₁, which is connected to theinput shaft Si via the electromagnetic clutch 54, rotates, the rotationis reduced in speed in the same direction, and output to the firstcarrier C₁.

The reduction ratio of the planetary type first planetary gear mechanismP₁ is defined as nc₁/ns₁, where ns₁ is an input rotational speed of thefirst sun gear ZS₁ and nc₁ is an output rotational speed of the firstcarrier C₁. If zs₁, zr₁, and zp₁ denote the numbers of teeth of thefirst sun gear ZS₁, the first ring gear ZR₁, and the first planetarygear ZP₁ respectively, the reduction ratio nc₁/ns₁ is given bync ₁ /ns ₁ =zs ₁/(zs ₁ +zr ₁).   (16)

The second planetary gear mechanism P₂ includes a second sun gear ZS₂, asecond ring gear ZR₂, a plurality of second planetary gears ZP₂, and asecond carrier C₂. The second sun gear ZS₂ is formed on the outerperiphery of the first carrier C₁ of the first planetary gear mechanismP₁. The second ring gear ZR₂ is formed integrally with the innerperiphery of the second support ring 43, which is fixed to the casing41. The second carrier C₂, which rotatably supports the second planetarygears ZP₂ meshing simultaneously with the second sun gear ZS₂ and thesecond ring gear ZR₂, is rotatably supported on the inner periphery ofthe second support ring 43 via a ball bearing 56. The second planetarygear mechanism P₂ is therefore of a planetary type in which the secondring gear ZR₂ is fixed and the second carrier C₂ is rotatable, and whenthe second sun gear ZS₂, which is an input member, rotates, the rotationis reduced in speed in the same direction, and output to the secondcarrier C₂.

The reduction ratio of the planetary type second planetary gearmechanism P₂ is defined as nc₂/ns₂, where ns₂ is an input rotationalspeed of the second sun gear ZS₂ and nc₂ is an output rotational speedof the second carrier C₂. If zs₂, zr₂, and zp₂ denote the number ofteeth of the second sun gear ZS₂, the second ring gear ZR₂, and thesecond planetary gear ZP₂ respectively, the reduction ratio nc₂/ns₂ isgiven bync ₂ /ns ₂ =zs ₂/(zs ₂ +zr ₂).   (17)

The third planetary gear mechanism P₃ includes a third sun gear ZS₃, athird ring gear ZR₃, a plurality of third planetary gears ZP₃, and athird carrier C₃. The third sun gear ZS₃ is formed integrally with theouter periphery of a central part of the second carrier C₂ of the secondplanetary gear mechanism P₂. The third ring gear ZR₃ is formedintegrally with the inner periphery of the first support ring 42, whichis fixed to the casing 41. The third carrier C₃, which rotatablysupports the third planetary gears ZP₃ meshing simultaneously with thethird sun gear ZS₃ and the third ring gear ZR₃, is rotatably supportedon the inner periphery of the first support ring 42 via a ball bearing57. The third planetary gear mechanism P₃ is therefore of a planetarytype in which the third ring gear ZR₃ is fixed and the third carrier C₃is rotatable, and when the third sun gear ZS₃, which is an input member,rotates, the rotation is reduced in speed in the same direction andoutput to the output shaft So, which is integral with the third carrierC₃.

The reduction ratio of the planetary type third planetary gear mechanismP₃ is defined as nc₃/ns₃, where ns₃ denotes an input rotational speed ofthe third sun gear ZS₃ and nc₃ denotes an output rotational speed of thethird carrier C₃. If zs₃, zr₃, and zp₃ denote the number of teeth of thethird sun gear ZS₃, the third ring gear ZR₃, and the third planetarygear ZP₃ respectively, the reduction ratio nc₃/ns₃ is given bync ₃ /ns ₃ =zs ₃/(zs ₃ +zr ₃).   (18)

Since the output rotational speed nc₁ of the first carrier C₁, which isthe output member of the first planetary gear mechanism P₁, is equal tothe input rotational speed ns₂ of the second sun gear ZS₂, which is theinput member of the second planetary gear mechanism P₂, and the outputrotational speed nc₂ of the second carrier C₂, which is the outputmember of the second planetary gear mechanism P₂, is equal to the inputrotational speed ns₃ of the third sun gear ZS₃, which is the inputmember of the third planetary gear mechanism P₃, the product of thereduction ratio nc₁/ns₁ of the first planetary gear mechanism P₁ shownin Equation (16), the reduction ratio nc₂/ns₂ of the second planetarygear mechanism P₂ shown in Equation (17), and the reduction rationc₃/ns₃ of the third planetary gear mechanism P₃ shown in Equation (18)is given by the ratio nc₃/ns₁ of the rotational speed nc₃ of the thirdcarrier C₃ of the third planetary gear mechanism P₃, the third carrierC₃ being the output member of the reduction gear 49, relative to therotational speed ns₁ of the first sun gear ZS₁ of the first planetarygear mechanism P₁, the first sun gear ZS₁ being the input member of thereduction gear 49.(nc ₁ /ns ₁)×(nc ₂ /ns ₂)×(nc ₃ /ns ₃)=nc ₃ /ns ₁   (19)

From Equation (16) to Equation (18), the reduction ratio nc₃/ns₁ of thereduction gear 49 is given bync ₃ /ns ₁ ={zs ₁/(zs ₁ +zr ₁)}×{zs ₂/(zs ₂ +zr ₂)}×{zs ₃/(zs ₃ +zr₃)}  (20)and in the embodiment, since the number of teeth of each gear is set asfollows:

zs₁ = 18 zp₁ = 27 zr₁ = 72 zs₂ = 96 zp₂ = 24 zr₂ = 144 zs₃ = 36 zp₃ = 54zr₃ = 144,the reduction ratio nc₃/ns₁ of the reduction gear 49 obtained bysubstituting these numbers of teeth in Equation (20) is 1/62.5. That is,when the input shaft Si of the reduction gear 49 rotates 62.5 times, theoutput shaft So rotates once in the same direction.

As hereinbefore described, since the reduction gear 49 is formed byconnecting the first to the third planetary gear mechanisms P₁ to P₃, itis possible to increase the torque of the motor 48 while ensuring thatthere is a sufficient reduction ratio. Furthermore, since the secondplanetary gear mechanism P₂ is disposed so as to overlap the radiallyouter side of the first planetary gear mechanism P₁, it is possible toreduce the thickness in the axis L direction of the reduction gear 49compared with a case in which the first to the third planetary gearmechanisms P₁ to P₃ are all disposed so as to be stacked in the axis Ldirection. That is, the first electric actuators 12 and the secondelectric actuators 13 can be made compact by suppressing the thicknessof the reduction gear 49 to a thickness corresponding to two planetarygear mechanisms while ensuring that there is a reduction ratiocorresponding to three planetary gear mechanisms, thereby enablingfitting lo under a user's clothing with a good appearance.

Although embodiments of the present invention are explained in detailabove, the present invention can be modified in a variety of wayswithout departing from the spirit and scope thereof.

For example, the reduction gear 49 of the first embodiment includes thefirst to the third planetary gear mechanisms P₁ to P₃, but the thirdplanetary gear mechanism P₃ may be omitted and only the first and secondplanetary gear mechanisms P₁ and P₂ may be employed.

Furthermore, in the first to the fourth embodiments, the electromagneticclutch 54 is disposed between the input shaft Si and the first sun gearZS₁, but the electromagnetic clutch 54 may be provided at any positionbetween the input shaft Si and the output shaft So.

INDUSTRIAL APPLICABILITY

As hereinbefore described, the present invention can be suitably appliedto a reduction gear for a walking assistance system assisting an injuredperson or an elderly person with weakened leg force to move.

1. A reduction gear for a walking assistance system that, in order toassist walking movement by extending/bending a user's leg joint, reducesthe speed of rotation of an input shaft (Si) driven by a motor (48) andtransmits the rotation to an output shaft (So) connected to the legjoint, the reduction gear comprising: the input shaft (Si), the outputshaft (So), a first planetary gear mechanism (P₁), and a secondplanetary gear mechanism (P₂) disposed coaxially on an axis (L), thesecond planetary gear mechanism (P₂) being disposed so as tosubstantially overlap the radially outer side of the first planetarygear mechanism (P₁), the rotation of the input shaft (Si) being reducedin speed by the first planetary gear mechanism (P₁) and the secondplanetary gear mechanism (P₂) and transmitted to the output shaft (So);the first planetary gear mechanism (P₁) comprising a first sun gear(ZS₁) provided on the input shaft (Si), a first ring gear (ZR₁)rotatably disposed so as to surround the outer periphery of the firstsun gear (ZS₁), a plurality of first planetary gears (ZP₁) meshingsimultaneously with the first sun gear (ZS₁) and the first ring gear(ZR₁), and a first carrier (C₁) rotatably supporting the first planetarygears (ZP₁), and; the second planetary gear mechanism (P₂) comprising asecond sun gear (ZS₂) provided on the outer periphery of the first ringgear (ZR₁), a second ring gear (ZR₂) disposed so as to surround theouter periphery of the second sun gear (ZS₂), a plurality of secondplanetary gears (ZP₂) meshing simultaneously with the second sun gear(ZS₂) and the second ring gear (ZR₂), and a second carrier (C₂)rotatably supporting the second planetary gears (ZP₂), wherein the firstcarrier (C₁) of the first planetary gear mechanism (P₁) is fixed to acasing (41), the second ring gear (ZR₂) of the second planetary gearmechanism (P₂) is fixed to the casing (41), and the second carrier (C₂)of the second planetary gear mechanism (P₂) is connected to the outputshaft (So).
 2. The reduction gear for the walking assistance systemaccording to claim 1, wherein a third planetary gear mechanism (P₃) isdisposed so as to be coaxial with and be stacked on the first planetarygear mechanism (P₁) and the second planetary gear mechanism (P₂) in theaxis (L) direction, the third planetary gear mechanism (P₃) comprising athird sun gear (ZS₃) provided on the outer periphery of a central partof the second carrier (C₂) of the second planetary gear mechanism (P₂),a third ring gear (ZR₃) fixed to the casing and disposed so as tosurround the outer periphery of the third sun gear (ZS₃), a plurality ofthird planetary gears (ZP₃) meshing simultaneously with the third sungear (ZS₃) and the third ring gear (ZR₃), and a third carrier (C₃)rotatably supporting the third planetary gear (ZP₃) and connected to theoutput shaft (So).
 3. A reduction gear for a walking assistance systemthat, in order to assist walking movement by extending/bending a user'sleg joint, reduces the speed of rotation of an input shaft (Si) drivenby a motor (48) and transmits the rotation to an output shaft (So)connected to the leg joint, the reduction gear comprising: the inputshaft (Si), the output shaft (So), a first planetary gear mechanism(P₁), and a second planetary gear mechanism (P₂) disposed coaxially onan axis (L), the second planetary gear mechanism (P₂) being disposed soas to substantially overlap the radially outer side of the firstplanetary gear mechanism (P₁), the rotation of the input shaft (Si)being reduced in speed by the first planetary gear mechanism (P₁) andthe second planetary gear mechanism (P₂) and transmitted to the outputshaft (So); the first planetary gear mechanism (P₁) comprising a firstsun gear (ZS₁) provided on the input shaft (Si), a first ring gear (ZR₁)rotatably disposed so as to surround the outer periphery of the firstsun gear (ZS₁), a plurality of first planetary gears (ZP₁) meshingsimultaneously with the first sun gear (ZS₁) and the first ring gear(ZR₁), and a first carrier (C₁) rotatably supporting the first planetarygears (ZP₁), and; the second planetary gear mechanism (P₂) comprising asecond sun gear (ZS₂) provided on the outer periphery of the first ringgear (ZR₁), a second ring gear (ZR₂) disposed so as to surround theouter periphery of the second sun gear (ZS₂), a plurality of secondplanetary gears (ZP₂) meshing simultaneously with the second sun gear(ZS₂) and the second ring gear (ZR₂), and a second carrier (C₂)rotatably supporting the second planetary gears (ZP₂), wherein the firstplanetary gear mechanism (P₁) is sandwiched between the first carrier(C₁) and the second carrier (C₂).
 4. The reduction gear for the walkingassistance system according to claim 3, wherein the first carrier (C₁)of the first planetary gear mechanism (P₁) is fixed to a casing (41),the second ring gear (ZR₂) of the second planetary gear mechanism (P₂)is fixed to the casing (41), and the second carrier (C₂) of the secondplanetary gear mechanism (P₂) is connected to the output shaft (So). 5.The reduction gear for the walking assistance system according to claim4, wherein a third planetary gear mechanism (P₃) is disposed so as to becoaxial with and be stacked on the first planetary gear mechanism (P₁)and the second planetary gear mechanism (P₂) in the axis (L) direction,the third planetary gear mechanism (P₃) comprising a third sun gear(ZS₃) provided on the outer periphery of a central part of the secondcarrier (C₂) of the second planetary gear mechanism (P₂), a third ringgear (ZR₃) fixed to the casing and disposed so as to surround the outerperiphery of the third sun gear (ZS₃), a plurality of third planetarygears (ZP₃) meshing simultaneously with the third sun gear (ZS₃) and thethird ring gear (ZR₃), and a third carrier (C₃) rotatably supporting thethird planetary gear (ZP₃) and connected to the output shaft (So). 6.The reduction gear for the walking assistance system according to claim3, wherein the first carrier (C₁) is part of a casing of the reductiongear.
 7. The reduction gear for the walking assistance system accordingto claim 3, wherein the first carrier (C₁) is non-rotatable.
 8. Thereduction gear for the walking assistance system according to claim 3,wherein the first carrier (C₁) has a diameter larger than a diameter ofthe second carrier (C₂).
 9. The reduction gear for the walkingassistance system according to claim 5, wherein the first carrier (C₁)has a diameter larger than a diameter of the third carrier (C₃).
 10. Thereduction gear for the walking assistance system according to claim 5,wherein a quantity of first planetary gears (ZP₁) is greater than aquantity of second planetary gears (ZP₂).
 11. The reduction gear for thewalking assistance system according to claim 3, enclosed in a casingthat is substantially cylindrical in shape, wherein the casing is formedby layering a first support ring, a second support ring, a supportplate, a motor housing, and a motor cover and integrally securing themwith a plurality of bolts.
 12. A reduction gear for a walking assistancesystem that, in order to assist walking movement by extending/bending auser's leg joint, reduces the speed of rotation of an input shaft (Si)driven by a motor (48) and transmits the rotation to an output shaft(So) connected to the leg joint, the reduction gear comprising: theinput shaft (Si), the output shaft (So), a first planetary gearmechanism (Pl), and a second planetary gear mechanism (P2) disposedcoaxially on an axis (L), the second planetary gear mechanism (P2) beingdisposed so as to substantially overlap the radially outer side of thefirst planetary gear mechanism (P1), the rotation of the input shaft(Si) being reduced in speed by the first planetary gear mechanism (P1)and the second planetary gear mechanism (P2) and transmitted to theoutput shaft (So); the first planetary gear mechanism (P1) comprising afirst sun gear (ZS1) provided on the input shaft (Si), a first ring gear(ZR1) rotatably disposed so as to surround the outer periphery of thefirst sun gear (ZS1), a plurality of first planetary gears (ZP1) meshingsimultaneously with the first sun gear (ZS1) and the first ring gear(ZR1), and a first carrier (C1) rotatably supporting the first planetarygears (ZP1), and; the second planetary gear mechanism (P2) comprising asecond sun gear (ZS2) provided on the outer periphery of the first ringgear (ZR0, a second ring gear (ZR2) disposed so as to surround the outerperiphery of the second sun gear (ZS2), a plurality of second planetarygears (ZP2) meshing simultaneously with the second sun gear (ZS2) andthe second ring gear (ZR2), and a second carrier (C2) rotatablysupporting the second planetary gears (ZP2), wherein the input shaft(Si), the first planetary gear mechanism (P1), the second planetary gearmechanism (P2), the motor are completely enclosed in a cylindricalcasing, and the first carrier (C1) of the first planetary gear mechanism(P1) is fixed to a casing (41), the second ring gear (ZR2) of the secondplanetary gear mechanism (P2) is fixed to the casing (41), and thesecond carrier (C2) of the second planetary gear mechanism (P2) isconnected to the output shaft (So).
 13. The reduction gear for thewalking assistance system according to claim 12, wherein a thirdplanetary gear mechanism (P3) is disposed so as to be coaxial with andbe stacked on the first planetary gear mechanism (P1) and the secondplanetary gear mechanism (P2) in the axis (L) direction, the thirdplanetary gear mechanism (P3) comprising a third sun gear (ZS3) providedon the outer periphery of a central part of the second carrier (C2) ofthe second planetary gear mechanism (P2), a third ring gear (ZR3) fixedto the casing and disposed so as to surround the outer periphery of thethird sun gear (ZS3), a plurality of third planetary gears (ZP3) meshingsimultaneously with the third sun gear (ZS3) and the third ring gear(ZR3), and a third carrier (C3) rotatably supporting the third planetarygear (ZP3) and connected to the output shaft (So).
 14. The reductiongear for the walking assistance system according to claim 12, whereinthe first carrier (C₁) is part of a casing of the reduction gear. 15.The reduction gear for the walking assistance system according to claim12, wherein the first carrier (C₁) is non-rotatable.
 16. The reductiongear for the walking assistance system according to claim 12, whereinthe first carrier (C₁) has a diameter larger than a diameter of thesecond carrier (C₂).